[Bug rtl-optimization/78041] Wrong code on ARMv7 with -mthumb -mfpu=neon-fp16 -O0

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78041

--- Comment #3 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Wilco from comment #2)
> (In reply to Bernd Edlinger from comment #1)
> > some background about this bug can be found here:
> > 
> > https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01561.html
> 
> The <shift>di3_neon pattern does not constrain the input not to overlap with
> the output for immediate shifts, and the arm_emit_coreregs_64bit_shift code
> does not handle partial overlaps. However it is feasible to fix that by
> swapping the order for the various cases.

from <shift>di3_neon:

            if (INTVAL (operands[2]) < 1)
              {
                emit_insn (gen_movdi (operands[0], operands[1]));
                DONE;
              }

Will the movdi pattern work with partial overlaps?
It does basically this:

      emit_move_insn (gen_lowpart (SImode, operands[0]),
                      gen_lowpart (SImode, operands[1]));
      emit_move_insn (gen_highpart (SImode, operands[0]),
                      gen_highpart (SImode, operands[1]));